Numerous means have been sought to improve the fuel-efficiency of moving bodies and, especially, moving bluff bodies by reducing their aerodynamic drag. In the field of surface transportation and, particularly in the long-haul trucking industry, even small improvements in fuel efficiency can reduce annual operating costs significantly. It is therefore advantageous in the design of a vehicle to reduce drag forces, thereby increasing the aerodynamic properties and efficiency of the vehicle.
The over-the-highway cargo-hauling tractor-trailer combination is one vehicle that experiences excessive aerodynamic drag. Generally described, tractor-trailer combinations typically include a tractor 18 having a so-called fifth wheel by which a box-like semi-trailer 24 may be attached to the tractor 18 by an articulated connection for transportation of the semi-trailer, as shown in FIG. 1.
It is well known that the aft ends of bluff bodies, such as trailers, are known to contribute significantly to aerodynamic drag, as evidenced by the formation of a wake 30 in the trailing region behind the trailer 24. The generation of the wake, formed by eddies, can be contributed to the shape of the conventional trailer, which is essentially a rectangular box having a flat, rectangular roof 38 and matching floor 40, along with flat, rectangular side panels 42. The fore and aft vertical surfaces 44 and 46 of such trailers are also generally flat rectangular surfaces. As such, current bluff bodies, such as trailer 24, which is suitable for use with tractors of the Class 8 type, suffer from a low-pressure zone at the rear of the trailer such that the air stream 50 suffers from early separation, resulting in a broad eddying wake 30 forming downstream of the separation, as best shown in FIG. 1. The net result is the creation of considerable aerodynamic drag.
Unfortunately, attempts to make the trailer shape more aerodynamic within the overall length of the trailer have been accompanied by reduced carrying capacity and interference during loading of the trailer. Additionally, attempts to make the rear of the trailer more aerodynamic, for example, by the addition of panels or inflatable bladders (not shown), can suffer from disadvantages such as added weight and a significant lengthening of the trailer, with associated reductions in fuel efficiency and more difficult handling characteristics.